1. Field of the Invention
The present invention relates to an endoscope system, and particularly, to an endoscope system capable of independently and simultaneously observing a forward field of view and a lateral field of view.
2. Description of the Related Art
An endoscope system is widely used in a medical field, an industrial field, and the like, the endoscope system including: an endoscope configured to pick up an image of a subject inside of a lumen such as a body cavity; an image processing apparatus configured to generate observation images of the subject picked up by the endoscope; and the like.
For example, Japanese Patent No. 3337682 discloses a wide-angle endoscope system including an endoscope, in which a forward observation lens configured to acquire a forward field of view image is provided on a distal end surface of a distal end portion of an insertion portion, and a plurality of lateral observation lenses configured to acquire lateral field of view images are provided in a circumferential direction of the distal end portion. Image pickup devices are further provided at respective image formation positions of the forward observation lens and the plurality of lateral observation lenses, and the image pickup devices pick up a forward field of view image and a plurality of lateral field of view images.
The wide-angle endoscope system is configured to independently obtain the forward field of view image and the plurality of lateral field of view images and is configured to display the independent images on one display means.
More specifically, when the images picked up by the respective image pickup devices are displayed on a monitor in the wide-angle endoscope system, the forward field of view image picked up by a forward observation image pickup device is arranged and displayed at a center, and the lateral field of view images picked up by a plurality of lateral observation image pickup devices, such as two lateral observation image pickup devices, are arranged and displayed on both sides of the forward field of view image, respectively.
By the way, in the wide-angle endoscope system described in Japanese Patent No. 3337682, a forward field of view image 516A picked up by the forward observation image pickup device is arranged and displayed at a center in a monitor screen 535 shown in FIG. 26, and lateral field of view images 516B and 516C picked up by the two lateral observation image pickup devices are arranged and displayed on both sides of the forward field of view image 516A, for example.
Note that in FIG. 26, it is assumed that “↑”, “⋆”, and “⋄” are schematically picked up for the forward field of view image 516A and the two lateral field of view images 516B and 516C, respectively.
Whether the forward field of view image 516A and the two lateral field of view images 516B and 516C (schematically illustrated by “↑”, “⋆”, and “⋄”, respectively) indicate directions and ranges corresponding to 517a, 517b, and 517c in FIG. 27a, respectively, or indicate positions and ranges corresponding to 517a′, 517b′, and 517c′ in FIG. 27b, respectively, is not clearly recognized. Note that reference signs 517d and 517d′ schematically illustrate an insertion portion distal end portion of the endoscope in FIGS. 27a and 27b, and a right direction corresponds to a forward direction of the insertion portion in FIGS. 27a and 27b. 
That is, as shown for example in FIG. 28, in an endoscope including one image pickup optical system and including only one display screen 416 displayed on a monitor screen 435, even when “↑”, “⋆”, and “⋄” are respectively lined up and displayed on the display screen (see left side in FIG. 28), directions and ranges of the images relative to the endoscope can be accurately imagined as indicated by reference sign 417 on a right side of FIG. 28.